Hazardous weather - anticyclones

Anticyclones are the opposite of depressions - they are an area of high atmospheric pressure where the air is sinking.

As the air is sinking, not rising, no clouds or rain are formed. This is because as the air sinks it warms, meaning it can hold more water.

The absence of fronts means winds may be very light. Consequently, high-pressure areas are often associated with settled, dry and bright conditions.

In summer, anticyclones bring dry, hot weather. In winter, clear skies may bring cold nights and frost. In cold conditions, anticyclones may also bring fog and mist. This is because the cold forces moisture in the air to condense at low altitudes.

A dusting of snow on grass with hedges visible in the background, under a blue sky
Notice the frost and the clear skies

The summer of 2017

Five men in shorts lean over some railings to cool themselves in the water a row of large fountains.

21 June 2017 was one of the hottest days in 41 years, with a temperature of 34.5°C (94°F) recorded at Heathrow.

The Met Office reading at the London airport was the highest in June since the mercury hit 35.6°C (96°F) in 1976 - the all-time high since records began.

The heatwave had seen five sizzling days in a row during which temperatures in parts of the UK topped 30°C. The reason for this is that high pressure (anticyclone conditions) brought hot air from the south which sat in place over the UK for 2-3 weeks.



  • Old age pensioners (OAPs) suffer during heatwaves.
  • A risk of heatstroke and sunburn increases, with longer term impacts of heat exhaustion and even skin cancer.
  • Water restrictions were put in place which limits availability to homes and businesses. In some regions of southern England hosepipe bans were introduced.
  • Hay fever sufferers have a difficult time with some temporarily hospitalised.


  • Rail and road services were disrupted because of a risk of ‘buckling’ on the lines.
  • Crops in southern England suffered drought which cost farmers millions in lost revenue.
  • Sick leave increases as people become too unwell to work or choose to take time off to enjoy the weather – so businesses suffer a reduction in incomes.


  • Vegetation dried up which led to wildlife issues. Birds and other insects are unable to find suitable habitats.
  • Areas with high traffic volumes experience a rise in pollution levels.
  • Reservoir and river levels drop to dangerous levels.